1.4.3 SI derived units with special names and symbols
Physical quantity
Name of
SI unit
Symbol for
SI unit
Expression in terms
of SI base units
frequency1
force
pressure, stress
energy, work, heat
power, radiant flux
electric charge
electric potential,
electromotive force
electric resistance
electric conductance
electric capacitance
magnetic flux density
magnetic flux
inductance
Celsius temperature2
luminous flux
illuminance
hertz
newton
pascal
joule
watt
coulomb
volt
Hz
N
Pa
J
W
C
V
s-1
m kg s-2
N m-2
Nm
J s-1
As
J C-1
ohm
siemens
farad
tesla
weber
henry
degree Celsius
lumen
lux
Ω
S
F
T
Wb
H
°C
lm
lx
V A-1
Ω-1
C V-1
V s m-2
Vs
V A-1 s
K
cd sr
cd sr m-2
= m-1 kg s-2
= m2 kg s-2
= m2 kg s-3
= m2 kg s-3 A-1
= m2 kg s-3 A-2
= m-2 kg-1 s3 A2
= m-2 kg-1 s4 A2
= kg s-2 A-1
= m2 kg s-2 A-1
= m2 kg s-2 A-2
(1)
For radial (angular) frequency and for angular velocity the unit rad s-1, or simply s-1,
should be used, and this may not be simplified to Hz. The unit Hz should be used
only for frequency in the sense of cycles per second.
(2)
The Celsius temperature θ is defined by the equation
θ/°C = T/K - 273.15
The SI unit of Celsius temperature is the degree Celsius, °C, which is equal to the
Kelvin, K. °C should be treated as a single symbol, with no space between the ° sign
and the letter C. (The symbol °K, and the symbol °, should no longer be used.)
Physical quantity
Name of
SI unit
activity3
becquerel
(radioactive)
adsorbed dose3
gray
(of radiation)
dose equivalent3
sievert
(dose equivalent index)
radian
plane angle4
4
solid angle
steradian
Symbol for
SI unit
Expression in terms
of SI base units
Bq
s-1
Gy
J kg-1
= m2 s-2
Sv
J kg-1
= m2 s-2
rad
sr
1
1
= m m-1
= m2 m-2
(3)
The units becquerel, gray, and sievert are admitted for reasons of safeguarding
human health.
(4)
The units radian and steradian are describe as 'SI supplementary units'. However,
in chemistry, as well as in physics they are usually treated as dimensionless
derived units, and this was recognized by CIPM in 1980. Since they are then of
dimension 1, this leaves open the possibility of including them or omitting them in
expressions of SI derived units. In practice this means that rad and sr may be used
when appropriate and may be omitted if clarity is not lost thereby.